Tiny Planet Mercury Shrinks Further

In a report published in the March 16th edition of Nature Geoscience, scientists revealed that the tiniest member of our Solar System, Mercury, is shrinking even further. According to lead researcher Paul Byrne from the Carnegie Institution of Washington, the small planet has contracted about seven kilometers (four miles), significantly more than revealed by previous findings.

The confirmation puts to rest a suspicion that researchers had harbored for a long time. That's because Mercury comprises of liquid iron core. As the planet cools, the metal turns into a solid state and therefore, contracts. The only way scientists could confirm their theory was to find evidence of deformation or wrinkles on the planet's surface as it accommodates to the smaller size, similar to what happens when grapes turn to raisins, or plums to prunes.

They got some proof when NASA's Mariner 10 spacecraft flew by Mercury in 1974 and 1975 and took a few images that showed strange 'lobate scarps' on the planet's surface. The deformation in its rocky skin was a clear sign that Mercury had shrunk. But since Mariner 10 took images of just 45% of the planet, scientists were able to confirm only between 1 to 2 km of shrinkage in radius.

The amount did not tally with their models which estimated that in its four billion years of existence, Mercury's radius should have shrunk a lot more. However, the scientists had no way to verify if they were right.

They therefore felt vindicated when NASA's Messenger Spacecraft which flew past Mercury in 2008 and 2009 and entered its orbit in 2011, was able to capture images of the rest of the planet that showed lobate scarps randomly covering its entire surface. Not only that, they also found wrinkles on the ridges of Mercury's volcanic plains, further proving it has been shrinking. These images also allowed the researchers to get a more accurate measure of the contraction.

Mercury is not the only planet that is becoming smaller. Scientists have observed similar wrinkles on the Moon and Mars. Thankfully, such shrinkage has not been observed on Earth. That's because unlike the other planets, which all comprise of just one-plate, Earth has a number constantly shifting tectonic plates. In addition, Mercury has a huge iron core - about 25,000 miles across and an extremely thin (260 miles) crust and mantle. In comparison, Earth's mantle is 1,800 miles thick, while its crust measures an average of 25 miles in depth.

Situated about 36 million miles or less than two-fifths the distance between the earth and sun, Mercury, bears the brunt of the heat from the star. Added to that is its large component of iron core, which helps attain unbearable temperatures. Surprisingly however, thanks to its deep craters which do get exposed to the sun, the small planet also harbors some of the coldest spots in the solar system. While the extreme heat makes it unable to sustain life, living on Mercury would be interesting given that a day would be as long as 59 earth days, while an entire year would be completed in a short 88 days. That's because the tiny planet is very slow at rotating around its own axis, but speedy quick when it comes to going around the sun.

Resources: universetoday.com, Space.com, LAtimes.com, news.discovery.com